The present invention relates to golf balls and more particularly to golf balls containing fillers.
Golf balls utilized in tournament or competitive play today are regulated for consistency purposes by the United States Golf Association (U.S.G.A.). In this regard, there are five (5) U.S.G.A. specifications which golf balls must meet under controlled conditions. These are size, weight, velocity, driver distance and symmetry.
Under the U.S.G.A. specifications, a golf ball can not weigh more than 1.62 ounces (with no lower limit) and must measure at least 1.68 inches (with no upper limit) in diameter. However, as a result of the openness of the upper or lower parameters in size and weight, a variety of golf balls can be made. For example, golf balls are manufactured today which by the Applicant are slightly larger (i.e., approximately 1.72 inches in diameter) while meeting the weight, velocity, distance and symmetry specifications set by the U.S.G.A.
Additionally, according to the U.S.G.A., the initial velocity of the ball must not exceed 250 ft/sec. with a 2% maximum tolerance (i.e., 255 ft/sec.) when struck at a set club head speed on a U.S.G.A. machine. Furthermore, the overall distance of the ball must not exceed 280 yards with a 6% tolerance (296.8 yards) when hit with a U.S.G.A. specified driver at 160 ft/sec. (clubhead speed) at a 10 degree launch angle as tested by the U.S.G.A. Lastly, the ball must pass the U.S.G.A. administered symmetry test, i.e., fly consistency (in distance, trajectory and time of flight) regardless of how the ball is placed on the tee.
While the U.S.G.A. regulates five (5) specifications for the purposes of maintaining golf ball consistency, alternative characteristics (i.e., spin, feel, durability, distance, sound, visibility, etc.) of the ball are constantly being improved upon by golf ball manufacturers. This is accomplished by altering the type of materials utilized and/or improving construction of the balls. For example, the proper choice of cover and core materials are important in achieving certain distance, durability and playability properties. Other important factors controlling golf ball performance include, but are not limited to, cover thickness and hardness, core stiffness (typically measured as compression), ball size and surface configuration.
As a result, a wide variety of golf balls have been designed and are available to suit an individual player""s game. Moreover, improved golf balls are continually being produced by golf ball manufacturers with technologized advancements in materials and manufacturing processes.
Two of the principal properties involved in a golf ball""s performance are resilience and compression. Resilience is generally defined as the ability of a strained body, by virtue of high yield strength and low elastic modulus, to recover its size and form following deformation. Simply stated, resilience is a measure of energy retained to the energy lost when the ball is impacted with the club.
In the field of golf ball production, resilience is determined by the coefficient of restitution (C.O.R.), the constant xe2x80x9cexe2x80x9d which is the ratio of the relative velocity of an elastic sphere after direct impact to that before impact.
Golf balls are typically described in terms of their size, weight, composition, dimple pattern, compression, hardness, durability, spin rate, and coefficient of restitution (COR). One way to measure the COR of a golf ball is to propel the ball at a given speed against a hard massive surface, and to measure its incoming and outgoing velocity. The COR is the ratio of the outgoing velocity to the incoming velocity and is expressed as a decimal between zero and one.
There is no United States Golf Association limit on the COR of a golf ball but the initial velocity of the golf ball must not exceed 250xc2x15 ft/second. As a result, the industry goal for initial velocity is 255 ft/ second, and the industry strives to maximize the COR without violating this limit.
The resilience or coefficient of restitution (COR) of a golf ball is the constant xe2x80x9ce,xe2x80x9d which is the ratio of the relative velocity of an elastic sphere after direct impact to that before impact. As a result, the COR (xe2x80x9cexe2x80x9d) can vary from 0 to 1, with 1 being equivalent to a perfectly or completely elastic collision and 0 being equivalent to a perfectly or completely inelastic collision.
COR, along with additional factors such as club head speed, club head mass, ball weight, ball size and density, spin rate, angle of trajectory and surface configuration (i.e., dimple pattern and area of dimple coverage) as well as environmental conditions (e.g. temperature, moisture, atmospheric pressure, wind, etc.) generally determine the distance a ball will travel when hit.
The COR in solid core balls is a function of the composition of the molded core and of the cover. The molded core and/or cover may be comprised of one or more layers such as in multi-layered balls. In balls containing a wound core (i.e., balls comprising a liquid or solid center, elastic windings, and a cover), the coefficient of restitution is a function of not only the composition of the center and cover, but also the composition and tension of the elastomeric windings. As in the solid core balls, the center and cover of a wound core ball may also consist of one or more layers.
The coefficient of restitution is the ratio of the outgoing velocity to the incoming velocity. In the examples of this application, the coefficient of restitution of a golf ball was measured by propelling a ball horizontally at a speed of 125xc2x15 feet per second (fps) and corrected to 125 fps against a generally vertical, hard, flat steel plate and measuring the ball""s incoming and outgoing velocity electronically. Speeds were measured with a pair of Oehler Mark 55 ballistic screens available from Oehler Research, Inc., P.O. Box 9135, Austin, Tex. 78766, which provide a timing pulse when an object passes through them. The screens were separated by 36xe2x80x3 and are located 25.25xe2x80x3 and 61.25xe2x80x3 from the rebound wall. The ball speed was measured by timing the pulses from screen 1 to screen 2 on the way into the rebound wall (as the average speed of the ball over 36xe2x80x3), and then the exit speed was timed from screen 2 to screen 1 over the same distance. The rebound wall was tilted 2 degrees from a vertical plane to allow the ball to rebound slightly downward in order to miss the edge of the cannon that fired it. The rebound wall is solid steel 2.0 inches thick.
As indicated above, the incoming speed should be 125xc2x15 fps but corrected to 125 fps. The correlation between COR and forward or incoming speed has been studied and a correction has been made over the xc2x15 fps range so that the COR is reported as if the ball had an incoming speed of exactly 125.0 fps.
The coefficient of restitution must be carefully controlled in all commercial golf balls if the ball is to be within the specifications regulated by the United States Golf Association (U.S.G.A.). As mentioned to some degree above, the U.S.G.A. standards indicate that a xe2x80x9cregulationxe2x80x9d ball cannot have an initial velocity exceeding 255 feet per second in an atmosphere of 75xc2x0 F. when tested on a U.S.G.A. machine. Since the coefficient of restitution of a ball is related to the ball""s initial velocity, it is highly desirable to produce a ball having sufficiently high coefficient of restitution to closely approach the U.S.G.A. limit on initial velocity, while having an ample degree of softness (i.e., hardness) to produce enhanced playability (i.e., spin, etc.).
PGA compression is another important property involved in the performance of a golf ball. The compression of the ball can affect the playability of the ball on striking and the sound or xe2x80x9cclickxe2x80x9d produced. Similarly, compression can effect the xe2x80x9cfeelxe2x80x9d of the ball (i.e., hard or soft responsive feel), particularly in chipping and putting.
Moreover, while compression itself has little bearing on the distance performance of a ball, compression can affect the playability of the ball on striking. The degree of compression of a ball against the club face and the softness of the cover strongly influences the resultant spin rate. Typically, a softer cover will produce a higher spin rate than a harder cover. Additionally, a harder core will produce a higher spin rate than a softer core. This is because at impact a hard core serves to compress the cover of the ball against the face of the club to a much greater degree than a soft core thereby resulting in more xe2x80x9cgrabxe2x80x9d of the ball on the clubface and subsequent higher spin rates. In effect the cover is squeezed between the relatively incompressible core and clubhead. When a softer core is used, the cover is under much less compressive stress than when a harder core is used and therefore does not contact the clubface as intimately. This results in lower spin rates.
The term xe2x80x9ccompressionxe2x80x9d utilized in the golf ball trade generally defines the overall deflection that a golf ball undergoes when subjected to a compressive load. For example, PGA compression indicates the amount of change in golf ball""s shape upon striking.
In the past, PGA compression related to a scale of from 0 to 200 given to a golf ball. The lower the PGA compression value, the softer the feel of the ball upon striking. In practice, tournament quality balls have compression ratings around 70-110, preferably around 80 to 100.
In determining PGA compression using the 0-200 scale, a standard force is applied to the external surface of the ball. A ball which exhibits no deflection (0.0 inches in deflection) is rated 200 and a ball which deflects {fraction (2/10)}th of an inch (0.2 inches) is rated 0. Every change of 0.001 of an inch in deflection represents a 1 point drop in compression. Consequently, a ball which deflects 0.1 inches (100xc3x970.001 inches) has a PGA compression value of 100 (i.e., 200-100) and a ball which deflects 0.110 inches (110xc3x970.001 inches) has a PGA compression of 90 (i.e., 200-110).
In order to assist in the determination of compression, several devices have been employed by the industry. For example, PGA compression is determined by an apparatus fashioned in the form of a small press with an upper and lower anvil. The upper anvil is at rest against a 200-pound die spring, and the lower anvil is movable through 0.300 inches by means of a crank mechanism. In its open position the gap between the anvils is 1.780 inches allowing a clearance of 0.100 inches for insertion of the ball. As the lower anvil is raised by the crank, it compresses the ball against the upper anvil, such compression occurring during the last 0.200 inches of stroke of the lower anvil, the ball then loading the upper anvil which in turn loads the spring. The equilibrium point of the upper anvil is measured by a dial micrometer if the anvil is deflected by the ball more than 0.100 inches (less deflection is simply regarded as zero compression) and the reading on the micrometer dial is referred to as the compression of the ball. In practice, tournament quality balls have compression ratings around 80 to 100 which means that the upper anvil was deflected a total of 0.120 to 0.100 inches.
An example to determine PGA compression can be shown by utilizing a golf ball compression tester produced by OK Automation, Sinking Spring, Pa. 19608 . The value obtained by this tester relates to an arbitrary value expressed by a number which may range from 0 to 100, although a value of 200 can be measured as indicated by two revolutions of the dial indicator on the apparatus. The value obtained defines the deflection that a golf ball undergoes when subjected to compressive loading. The OK Automation test apparatus consists of a lower movable platform and an upper movable spring-loaded anvil. The dial indicator is mounted such that it measures the upward movement of the springloaded anvil. The golf ball to be tested is placed in the lower platform, which is then raised a fixed distance. The upper portion of the golf ball comes in contact with and exerts a pressure on the springloaded anvil. Depending upon the distance of the golf ball to be compressed, the upper anvil is forced upward against the spring.
Alternative devices have also been employed to determine compression. For example, Applicant also utilizes a modified Riehle Compression Machine originally produced by Riehle Bros. Testing Machine Company, Phil., Pa. to evaluate compression of the various components (i.e., cores, mantle cover balls, finished balls, etc.) of the golf balls. The Riehle compression device determines deformation in thousandths of an inch under a fixed initialized load of 200 pounds. The selection of an appropriate anvil for use in making a measurement is based upon the diameter of the component which is to be measured. Using such a device, a Riehle compression of 61 corresponds to a deflection under load of 0.061 inches.
Additionally, an approximate relationship between Riehle compression and PGA compression exists for balls of the same size. It has been determined by Applicant that Riehle compression corresponds to PGA compression by the general formula PGA compression=160-Riehle compression. Consequently, 80 Riehle compression corresponds to 80 PGA compression, 70 Riehle compression corresponds to 90 PGA compression, and 60 Riehle compression corresponds to 100 PGA compression. For reporting purposes, Applicant""s compression values are usually measured as Riehle compression.
Furthermore, additional compression devices may also be utilized to monitor golf ball compression so long as the correlation to PGA compression is known. These devices have been designed, such as a Whitney Tester, to correlate or correspond to PGA compression through a set relationship or formula.
Additionally, cover hardness and thickness are important in producing the distance, playability and durability properties of a golf ball. As mentioned above, cover hardness directly affects the resilience and thus distance characteristics of a ball. All things being equal, harder covers produce higher resilience. This is because soft materials detract from resilience by absorbing some of the impact energy as the material is compressed on striking.
Furthermore, soft covered balls are preferred by the more skilled golfer because he or she can impact high spin rates that give him or her better control or workability of the ball. Spin rate is an important golf ball characteristic for both the skilled and unskilled golfer. As just mentioned, high spin rates allow for the more skilled golfer, such as PGA and LPGA professionals and low handicap players, to maximize control of the golf ball. This is particularly beneficial to the more skilled golfer when hitting an approach shot to a green. Thus, the more skilled golfer generally prefers a golf ball exhibiting high spin rate properties.
However, a high spin golf ball is not desired by all golfers, particularly high handicap players who cannot intentionally control the spin of the ball. Additionally, since a high spinning ball will roll substantially less than a low spinning golf ball, a high spinning ball is generally short on distance.
In this regard, less skilled golfers, have, among others, two substantial obstacles to improving their game: slicing and hooking. When a club head meets a ball, an unintentional side spin is often imparted which sends the ball off its intended course. The side spin reduces one""s control over the ball as well as the distance the ball will travel. As a result, unwanted strokes are added to the game.
Consequently, while the more skilled golfer frequently desires a high spin golf ball, a more efficient ball for the less skilled player is a golf ball that exhibits low spin properties. The low spin ball reduces slicing and hooking and enhances distance. Furthermore, since a high spinning ball is generally short on distance, such a ball is not universally desired by even the more skilled golfer.
With respect to high spinning balls, up to approximately twenty years ago, most high spinning balls were comprised of balata or blends of balata with elastomeric or plastic materials. The traditional balata covers are relatively soft and flexible. Upon impact, the soft balata covers compress against the surface of the club producing high spin. Consequently, the soft and flexible balata covers provide an experienced golfer with the ability to apply side spin to control the ball in flight in order to produce a draw or a fade, or a backspin which causes the ball to xe2x80x9cbitexe2x80x9d or stop abruptly on contact with the green.
Moreover, the soft balata covers produce a soft xe2x80x9cfeelxe2x80x9d to the low handicap player. Such playability properties (workability, feel, etc.) are particularly important in short iron play with low swing speeds and are exploited significantly by relatively skilled players.
However, despite all the benefits of balata, balata covered golf balls are easily cut and/or damaged if mis-hit. Golf balls produced with balata or balata-containing cover compositions therefore have a relatively short lifespan.
Additionally, soft balata covered balls are shorter in distance. While the softer materials will produce additional spin, this is frequently produced at the expense of the initial velocity of the ball. Moreover, as mentioned above, higher spinning balls tend to roll less.
As a result of these negative properties, balata and its synthetic substitutes, transpolyisoprene and trans-polybutadiene, have been essentially replaced as the cover materials of choice by new synthetic materials. Included in this group of materials are ionomer resins.
Ionomeric resins are polymers in which the molecular chains are cross-linked by ionic bonds. As a result of their toughness, durability and flight characteristics, various ionomeric resins sold by E.I. DuPont de Nemours and Company under the trademark xe2x80x9cSurlyn(copyright)xe2x80x9d and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks xe2x80x9cEscor(copyright)xe2x80x9d and xe2x80x9clotek(copyright)xe2x80x9d, have become the materials of choice for the construction of golf ball covers over the traditional xe2x80x9cbalataxe2x80x9d (transpolyisoprene, natural or synthetic) rubbers. As stated, the softer balata covers, although exhibiting enhanced playability properties, lack the durability (cut and abrasion resistance, fatigue endurance, etc.) properties required for repetitive play and are limited in distance.
Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic group in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e., durability, etc., for golf ball cover construction over balata.
Historically, some of the advantages produced by ionomer resins in increased durability were offset to some degree by decreases produced in playability. This was because although the ionomeric resins were very durable, they initially tended to be very hard when utilized for golf ball cover construction, and thus lacked the degree of softness required to impart the spin necessary to control the ball in flight. Since the initial ionomeric resins were harder than balata, the ionomeric resin covers did not compress as much against the face of the club upon impact, thereby producing less spin.
In addition, the initial, harder and more durable ionomeric resins lacked the xe2x80x9cfeelxe2x80x9d characteristic associated with the softer balata related covers. The ionomer resins tended to produce a hard responsive xe2x80x9cfeelxe2x80x9d when struck with a golf club such as a wood, iron, wedge or putter.
As a result of these difficulties and others, a great deal of research has been and is currently being conducted by golf ball manufacturers in the field of ionomer resin technology. There are currently more than fifty (50) commercial grades of ionomers available both from DuPont and Exxon, with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e., relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcement agents, etc. However, a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the improved impact resistance and carrying distance properties produced by the xe2x80x9chardxe2x80x9d ionomeric resins, but also the playability (i.e., xe2x80x9cspinxe2x80x9d, xe2x80x9cfeelxe2x80x9d, etc.) characteristics previously associated with the xe2x80x9csoftxe2x80x9d balata covers, properties which are still desired by the more skilled golfer.
Consequently, a number of two-piece (a solid resilient center or core with a molded cover) and three-piece (a liquid or solid center, elastomeric winding about the center, and a molded cover) golf balls have been produced by the Applicant and others to address these needs. The different types of materials utilized to formulate the cores, covers, etc. of these balls dramatically alters the balls"" overall characteristics.
One of the ways to affect spin of a golf ball is to transfer weight toward or away from the center of the ball. A golf ball with increased perimeter weighting has an increased moment of inertia and/or a greater radius of gyration and thus generates lower initial spin than a golf ball with increased weighting of the center or core. A ball with increased perimeter weighting also has greater spin retention than a ball with conventional weighting. The present invention is directed to a high moment of inertia golf ball which has a relatively low spin rate.
An object of the invention is to provide a low spin golf ball with a high COR.
Another object of the invention is to provide a golf ball which will travel a long distance.
A further object of the invention is to provide a method of making a low spin golf ball.
Other objects will be in part obvious and in part pointed out more in detail hereafter.
The invention in a preferred form is a golf ball comprising a solid core formed from a rubber material and 0.1-40 parts by weight of a filler material having a specific gravity of at least 7 based upon 100 parts by weight of the rubber material, and a dimpled cover layer comprising an ionomeric resin and at least 2.5 parts by weight of a whitening agent selected from the group consisting of titanium dioxide, barium sulfite, and zinc sulfide white based upon 100 parts by weight of the resin, the golf ball having a coefficient of restitution of at least 0.750. The core of the golf ball preferably has 1-4 volume percent, and more preferably 1-2.5 volume percent more rubber than a core which contains zinc oxide filler in place of the high specific gravity filler and has the same weight and Riehle compression.
In a particularly preferred form of the invention, the filler material is tungsten. The whitening agent most preferably is titanium dioxide. The whitening agent preferably is present in an amount of 5-10 parts by weight based upon 100 parts by weight of the resin. The dimpled cover layer preferably comprises ionomer.
The solid core can have a cover layer formed directly thereon or can be surrounded by a layer of windings. An inner cover layer can be included beneath the dimpled cover layer.
Another preferred form of the invention is a golf ball comprising a solid core formed from a rubber material and 0.1-40 parts by weight of tungsten based upon 100 parts by weight of the rubber material, and a dimpled cover layer comprising an ionomeric resin and at least 2.5 parts by weight of titanium dioxide based upon 100 parts by weight of the resin. The resin used to form the golf ball cover preferably comprises ionomer. The golf ball preferably has a coefficient of restitution of at least 0.750.
Yet another preferred form of the invention is a golf ball comprising a solid core comprising a rubber material and 10-30 parts by weight of at least one member selected from the group consisting of tungsten, bismuth, and molybdenum based upon 100 parts by weight of the rubber material, and a dimpled cover layer comprising a resin composition which includes ionomer and 2.5-20 parts by weight of titanium dioxide based upon 100 parts by weight of the resin composition.